A sport ball may have a plurality of panels that are joined at seams to form a casing. The panels may include a thermoplastic polymer material applied to an interior side of the panels, and the thermoplastic polymer material may be heat-activated to extend across the seams. The ball may further include a bladder within the casing and an intermediate layer located between the casing and the bladder. The thermoplastic polymer material may also be heat-activated to bond with the intermediate layer or casing.